Hematopoietic progenitor kinase 1 (HPK1) originally cloned from hematopoietic progenitor cells is a member of MAP kinase kinase kinase kinases (MAP4Ks) family, which includes MAP4K1/HPK1, MAP4K2/GCK, MAP4K3/GLK, MAP4K4/HGK, MAP4K5/KHS, and MAP4K6/MINK (Hu, M. C., et al., Genes Dev, 1996. 10(18): p. 2251-64). HPK1 is of particular interest because it is predominantly expressed in hematopoietic cells such as T cells, B cells, macrophages, dendritic cells, neutrophils, and mast cells (Hu, M. C., et al., Genes Dev, 1996. 10(18): p. 2251-64; Kiefer, F., et al., EMBO J, 1996. 15(24): p. 7013-25). HPK1 kinase activity has been shown to be induced upon activation of T cell receptors (TCR) (Liou, J., et al., Immunity, 2000. 12(4): p. 399-408), B cell receptors (BCR) (Liou, J., et al., Immunity, 2000. 12(4): p. 399-408), transforming growth factor receptor (TGF-βR) (Wang, W., et al., J Biol Chem, 1997. 272(36): p. 22771-5; Zhou, G., et al., J Biol Chem, 1999. 274(19): p. 13133-8), or Gs-coupled PGE2 receptors (EP2 and EP4) (Ikegami, R., et al., J Immunol, 2001. 166(7): p. 4689-96). As such, HPK1 regulates diverse functions of various immune cells.
HPK1 is important in regulating the functions of various immune cells and it has been implicated in autoimmune diseases and anti-tumor immunity (Shui, J. W., et al., Nat Immunol, 2007. 8(1): p. 84-91; Wang, X., et al., J Biol Chem, 2012. 287(14): p. 11037-48). HPK1 knockout mice were more susceptible to the induction of experimental autoimmune encephalomyelitis (EAE) (Shui, J. W., et al., Nat Immunol, 2007. 8(1): p. 84-91). In human, HPK1 was downregulated in peripheral blood mononuclear cells of psoriatic arthritis patients or T cells of systemic lupus erythematosus (SLE) patients (Batliwalla, F. M., et al., Mol Med, 2005. 11(1-12): p. 21-9). Those observations suggested that attenuation of HPK1 activity may contribute to autoimmunity in patients. Furthermore, HPK1 may also control anti-tumor immunity via T cell-dependent mechanisms. In the PGE2-producing Lewis lung carcinoma tumor model, the tumors developed more slowly in HPK1 knockout mice as compared to wild-type mice (see US 2007/0087988). In addition, it was shown that adoptive transfer of HPK1 deficient T cells was more effective in controlling tumor growth and metastasis than wild-type T cells (Alzabin, S., et al., Cancer Immunol Immunother, 2010. 59(3): p. 419-29). Similarly, BMDCs from HPK1 knockout mice were more efficient to mount a T cell response to eradicate Lewis lung carcinoma as compared to wild-type BMDCs (Alzabin, S., et al., J Immunol, 2009. 182(10): p. 6187-94). These data, in conjunction with the restricted expression of HPK1 in hematopoietic cells and lack of effect on the normal development of immune cells, suggest that HPK1 may be an excellent drug target for enhancing antitumor immunity. Accordingly, there is a need for new compounds that modulate HPK1 activity.